The present invention relates to frozen low-fat food emulsions, particularly to low-fat oil-in-water emulsions, and to processes for preparing these emulsions.
Although an increasing number of consumers prefer low-fat food products over full fat food products, it is difficult for manufacturers of low-fat products to replicate the desired flavour of full-fat products. This difficulty is particularly a problem in frozen low-fat food products such as ice-creams, and other low-fat food products.
It has been demonstrated that lowering the fat content of foods gives rise to flavour imbalance, as the rate of flavour release is greater in fat-reduced foods; in this respect, reference is made to an article by Shamil et al in Food Quality and Preference 1991/2, 3 (1) 51-60 entitled xe2x80x9cFlavour release and perception in reduced-fat foodsxe2x80x9d.
The greater rate of flavour release in reduced-fat frozen oil-in-water food emulsions is demonstrated by the present inventors in FIG. 1, which is a graph of profiles of flavour intensity against time for non-aerated ice-creams having different levels of fat (see in particular line 7 (0.5 wt % fat) and line-1 (12.8. wt % fat)).
During oral processing, full-fat (eg 12.8 wt % fat) ice-creams exhibit a gradual build up of flavour to a low peak of maximum flavour impact, followed by a slow dissipation of flavour. In contrast, traditional very low-fat/zero-fat (less than 3 wt % fat) ice-creams exhibit a rapid dissipation of flavour creating a very high peak of maximum flavour impact at an early stage of oral processing.
The same greater rate of flavour release in reduced-fat food products also occurs in the oral processing of full fat versus low fat non-frozen food emulsions, as is known from our co-pending application PCT/EP98/00645.
The profile exhibited by full-fat frozen products eg ice-creams equates to a taste and mouthfeel that are preferred by consumers; the profile exhibited by equivalent low-fat products equates to a flavour which is initially too intense, with no pleasing aftertaste.
Many important flavour molecules are lipophilic i.e. hydrophobic. As fat levels are reduced in oil-in-water emulsions, a greater proportion of these flavour molecules are found in the water phase. When the emulsion is broken down, eg in the mouth during eating, the hydrophobic nature of the flavour molecules results in their rapid release into nasal airspace.
Developments in flavour technology have resulted in flavour molecules being encapsulated to control flavour release and to stabilise and protect the molecules. Commonly-used encapsulation techniques include spray-drying, bed fluidisation and coacervation. (See the reference xe2x80x9cEncapsulation and Controlled Releasexe2x80x9d by Karsa and Stephensen, Royal Soc Chem, ISBN 0.85/86-6/5-8.)
These techniques involve entrapping a flavour molecule within a covering or microcapsule. The resulting encapsulated product is often in the form of small dry particles, which are added to foodstuffs. Upon heating or eating the foodstuffs, the particles are thermally or physically broken down to release the flavour molecules. The release is normally rapid.
U.S. Pat. No. 5 498 439 discloses encapsulating flavour oils in a colloid gel, which is made from water and animal protein polymers or plant polysaccharides. The flavour oil is mixed with the gel components under high shear pressure to create a stable colloid gel matrix, in which the flavour oil is physically encapsulated and retained by the hydrophilic nature of the gel. A solution of the encapsulated flavour oil may be injected into meat to impart flavour thereto.
Our co-pending patent application PCT/EP98/00645 discloses non-frozen low-fat food emulsions having a rate of flavour release which is comparable to that of the equivalent full-fat non-frozen food emulsions. In particular it discloses a non-frozen low-fat food emulsion comprising a continuous aqueous phase and a dispersed phase which comprises fat particles, gel particles and fat-soluble flavour particles with the rate of release of the flavour molecules from the emulsion being delayed to provide a similar release rate to that of the corresponding full fat product.
The present invention seeks to provide a frozen low-fat food emulsion having a rate of flavour release which is comparable to that of a full-fat frozen food emulsion, thereby creating a frozen low-fat food emulsion having the flavour of a frozen full-fat food emulsion.
According to a first aspect of the present invention there is provided a frozen low-fat food emulsion comprising a continuous aqueous phase and a dispersed phase which comprises fat particles, gel particles and fat-soluble flavour molecules, wherein substantially all of the fat particles are located within the gel particles, and wherein at least 35% of the flavour molecules are located in a plurality of the gel particles to thereby delay the rate of release of the flavour molecules from the frozen emulsion.
It is preferred that at least 50% of the flavour molecules are located in a plurality of the gel particles, and most preferably at least 60% are so located.
The actual proportion of flavour molecules which are located in the gel particles will depend on the oil/water partition coefficient of the flavour molecules concerned. In the above, it is preferred that a plurality (i.e. more than 50%) of the flavour molecules are located in a plurality of the gel particles (which may be the case when the flavour molecule has a better solubility in oil than in water). The higher the percentage of the flavour molecules that is located in the gel particles, the better is the delayed release effect obtained.
For the purpose of the present invention, fat-soluble flavour molecules include flavour molecules which are totally soluble in fat or oil, and flavour molecules which are only partially soluble in fat or oil.
xe2x80x98Frozenxe2x80x99 as used herein refers to emulsions that contain part of their composition as ice. The characteristic temperature at which ice forms is dependent on the amount of soluble components in the composition. Typically the temperature at which ice forms in the composition, or at which freezing occurs, is in the range of 0xc2x0 C. to xe2x88x925xc2x0 C., but it may be lower, e.g. 5xc2x0 C. to xe2x88x9220xc2x0 C. if a high solids (especially sugar) content is used. The frozen emulsion is designed to be stored and/or consumed with an ice-phase present.
The frozen low-fat emulsions of the present invention have a continuous aqueous phase (which may be in a partially or fully frozen state in the frozen product) and a dispersed phase which comprises fat particles, gel particles and flavour molecules. Any food product that is frozen and has the above structure is encompassed by the term xe2x80x9cfrozen (low-fat) food emulsionxe2x80x9d as used herein.
Also, it is herein to be understood that the present invention is limited (application in) to frozen emulsions. Examples include ice-creams, sherbet, frozen custards, frozen yoghurts, frozen mousses, and other conventionally fat containing frozen (emulsion) confections. A list of typical frozen food products is given in xe2x80x9cIce-creamxe2x80x9d, by Arbuckle 4th edition, Appendix B and E, published by Van Nostrand Reinhold Company. Also covered by xe2x80x9cfrozen emulsionsxe2x80x9d are frozen xe2x80x9cmicrostructured emulsionsxe2x80x9d. Furthermore within the term frozen-emulsions as used herein are encompassed frozen food products that are not conventionally produced as emulsions such as e.g. water ices, sorbets and frozen fruit purees, but which will be in the form of a frozen emulsion when produced in accordance with the invention.
It is to be understood that the term xe2x80x9cfrozen food emulsionsxe2x80x9d as used herein includes all such suitable emulsions. Also encompassed by the term xe2x80x9cfrozen emulsionsxe2x80x9d as used herein are water ices, sorbets and other conventionally fat free food products having a fat ingredient added thereto. In certain circumstances it may be desirable to include a fat-containing component in a water ice or sorbet, etc., for example to produce a xe2x80x98creamyxe2x80x99 or xe2x80x98milkyxe2x80x99 texture, or to allow the introduction of fat-soluble flavours. In such cases, where fat is present in a conventionally fat free product, the water ice or sorbet, etc., falls within the scope of the present invention.
By the term xe2x80x98low-fatxe2x80x99 as used herein is meant those food emulsions as defined above that have a reduced total fat content when compared to the traditional full-fat version of that product. However, within this definition it is to be appreciated that the term xe2x80x98low-fatxe2x80x99 covers a wide range of possible fat contents, dependant upon the fat content of the full-fat product. Whilst ice-creams are used to exemplify the definition , it will be appreciated that for a higher fat content full fat product, e.g. Cream, the low-fat version may contain relatively high fat levels, e.g. 30 wt % fat. For example, traditional full fat ice-creams typically have a fat content in the range 5-16 wt %, whereas, a low-fat ice-cream typically has a fat content in the range 0-8% total fat.
For the term xe2x80x98low fatxe2x80x99 as used herein the restriction applies that for a given full fat formulation the fat content is reduced in the equivalent low-fat formulation. In other words, a full fat traditional ice-cream formulation containing 16 wt % total fat may be produced as a low fat variety containing 8 wt % fat, even though this wt % fat falls within the range that may be encountered for other full-fat ice-creams.
For products that do not always conventionally contain fat, e.g. water ices and sorbets etc., but for which it may be desirable to add fat in some certain circumstances (eg to provide a different fat-soluble flavour or to make a milk-ice), the term xe2x80x98low-fatxe2x80x99 as used herein applies to products containing less than 5 wt % fat.
The frozen low-fat food emulsions of the invention are the emulsions per se, e.g. a low-fat ice-cream. Furthermore, the frozen low-fat food emulsions of the invention may form part of any composite food product such as e.g. a coated ice-cream or an ice-cream filled wafer, etc. The whole, or just the emulsion part of the composite product may be frozen.
The frozen low-fat food emulsions, and composite products containing the emulsions, will typically comprise other conventional food product ingredients such as those selected from colourants, fruit pieces, nut pieces, sauces and couvertures etc., as appropriate.
The frozen low-fat food emulsions of the present invention may be either aerated or non-aerated emulsions as required. It is preferred that if the emulsion is an aerated ice-cream, in other words it has a % overrun of greater than 1%, it has an overrun in the range of 5-200% more preferably 10-150%, for example 15-140%, or e.g. 18-130%.
The gel particles are prepared from one or more food grade gel-forming biopolymers, preferably selected from proteins (eg casein) galactans (eg agar, carrageenans, furcelleran), galactomannans (eg guar gum, locust bean gum, tara gum, fenugreek), glucomannans (eg konjac mannan), galacturonates (eg pectins), glucans (eg starches and curdlan), uronates (eg alginate), exopolysaccharides (eg xanthan, gellan), natural gum exudates (eg gum acacia, gum arabic), gelatin and mixtures thereof.
Mixtures of proteins and polysaccharides are preferred as they may interact associatively, disassociatively or synergistically.
The frozen low-fat emulsion of the present invention may comprise between 0 and 30 wt % fat. Preferably the amount of fat is greater than 0.005 wt % but is less than 20 wt % fat, more preferably less than 10 wt % fat, e.g. less than 8 wt %. For example 0.01-10 wt % fat, especially 0.1-8 wt % fat is preferred. In a preferred embodiment, the emulsion comprises from 0.01 wt % fat; more preferably at least 0.5 wt % fat. Within the above ranges the wt % fat may vary according to the particular type of frozen emulsion.
For example in a low-fat ice-cream the wt % fat may be 0 to 8 wt %, preferably 0.1-7 wt %, more preferably 1-6.5 wt %. However in a fat containing water ice or sorbet the wt % fat will typically be within the range eg 0.01% to 4.5%, especially 0.1% to 3 wt %, or e.g. less than 2 wt %.
For the purpose of the present invention, the definition of fat includes liquid oil, crystallising fat blends, e.g. butter fat, and fat mimics such as sucrose polyesters. The oil of fat may be solid or liquid at room temperature. Any suitable edible oil or fat may be used in the formation of the gel particles. Examples include sunflower oil, rapeseed oil and other vegetable or nut oils.
The frozen low-fat emulsion of the present invention may comprise from 0.1 to 60% by volume of gel particles, preferably from 0.2 to 40%, most preferably 0.25-30%, or e.g. 20%. The % by volume of beads in the product will vary according to the wt % of fat or oil in the beads. A higher wt% of fat or oil in the beads requires a lower % by volume of beads in the product to provide the desired wt % in the product.
The gel particles may have a volume average size of from at least 30, preferably at least 50, more preferably at least 100 microns to less than 5000 microns, preferably less than 1000 microns, more preferably less than 500 microns, or e.g. in the range 50-5000 microns, preferably 60-500 microns. Within these ranges, larger particle sizes are preferred. It has been typically found that the larger the gel particle size, the slower the rate of flavour release.
The inventors of the claimed emulsion were surprised to find that the presence of gel particles delays the release of flavour molecules during oral processing; this is surprising because the flavour molecules are of a size suitable for diffusing through the gel matrix of the particles. (It is even more surprising that the freezing of the food product emulsion does not negate or inhibit this effect during oral processing). It is therefore understood that, in the present invention, the gel particles do not encapsulate the flavour molecules in the traditional sense, since the flavour molecules are not trapped within the gel particles.
Without wishing to be bound by theory, the inventors believe that the gel particles act as a static region within the mobile aqueous phase of the emulsion (when eaten the aqueous phase melts in the mouth).
As many important flavour molecules are lipophilic (fat-soluble) they have a preference for solubilising in the oil droplets. The rationale behind this approach is that in o/w emulsions the release of lipophilic flavours occurs in the sequence oilxe2x86x92waterxe2x86x92air. It is therefore possible to control the release of lipophillic flavours by creating barriers around the oil droplets which hinder their release into the aqueous phase when the frozen emulsion melts either totally, substantially, or partially during eating. Microstructured emulsions do this by increasing the diffusional pathway and reducing the rate at which lipophillic flavours are released into the aqueous phase.
In accordance with the present invention, there is also provided a process for the preparation of a frozen low-fat food emulsion comprising the steps of:
a) admixing fat and a gel-forming biopolymer to form a first liquid phase;
b) adding the first liquid phase to a second liquid phase which promotes gel formation of the biopolymer to form gel particles having particles of fat located therein;
c) mixing the gel particles with an aqueous phase and fat-soluble flavour molecules to form an aqueous-continuous emulsion; and
d) subjecting the aqueous-continuous emulsion to freezing conditions so that the frozen low-fat emulsion is produced.
Optionally, the first liquid phase is emulsified prior to step (b). In step (b), the first liquid phase may be injected into the second liquid phase. Alternatively, in step (b), the first liquid phase may be sprayed on to the second liquid phase.
The second liquid phase may have a lower temperature than the first liquid phase in order to effect gel formation. Alternatively, the second liquid phase may react with the biopolymer in the first liquid phase in order to effect gel formation.
It is also possible, according to the present invention, to subject the gel particles, and/or aqueous phase, and/or fat-soluble flavour molecules to freezing conditions prior to producing the final frozen emulsion in step (b) above.
The gel particles of the invention may be made by any suitable conventional method.
In one method of preparing the gel particles, an emulsion of agar and/or alginate and oil is injected into a cooled stream of xanthan gum in a low speed mixer; the lower temperature of the xanthan gum promotes gelation of the agar. The resulting gel particles may be used to prepare a low-fat emulsion that is frozen to produce a frozen low-fat emulsion, such as for example a low-fat ice-cream. The size of the particles is determined by the amount of shear.
In another method of preparing the gel particles, an emulsion of sodium alginate and/or agar and oil is co-extruded with air through a nozzle into a bath of calcium chloride solution; the calcium ions react with the alginate to form particles of calcium alginate gel. The size of the gel particles may be determined by the flow rate of the co-extrudate The resulting gel particles may be used as referred to in the preceding paragraph.
In another method of preparing the gel particles an emulsion of sodium alginate is injected into a stream of calcium chloride solution (or calcium chloride and xanthan gum) in a low speed mixer. The size of the particles is determined by the amount of shear. The resulting gel particles may be used as stated above.
In particular an example of forming the gel particles is given in example 1, and is applicable to gel particles to be used in all frozen emulsions of the invention.
The gel particles may in certain circumstances contain up to 60 wt % of oil or fat, preferably 2 to 55 wt %, especially 4 to 40 wt %, e.g. 5 to 35 wt %, or 5 to 30 wt %. However generally 5 to 30 wt % is preferred. For example, good results have been obtained with gel particles containing 5, 10 and 20 wt % fat. However, the level of fat or oil in the beads is not believed to be as important as the total fat -content in the product.
The low-fat emulsions of the present invention may be formed by any suitable method, as long as substantially intact gel particles remain in the final product. In general the process methods known in the art for the traditional full or low-fat products are appropriate. More typically the frozen food emulsion will be formed by conventional methods used for the product concerned. For example low-fat ice-creams may be produced by conventional ice-cream production methods, including those having homogenisation and/or pasteurisation stages. The examples give details of suitable methods of making frozen low-fat emulsions according to the invention for ice-cream and water-ices. However, any suitable known method of preparation may be used, as the method of preparation of the product is not critical. The method of preparation may include an aeration step to produce an aerated product. The process may be a continuous or batch process.
The frozen low-fat emulsions food products of the present invention may be frozen by any suitable method to produce the frozen product. The freezing may for example take place quiescently, e.g. in a blast freezer. Alternatively, the freezing may occur with agitation eg in a scraped surface heat exchanger. Typically the freezing takes place at a temperature of 0xc2x0 C. to xe2x88x9230xc2x0 C., for example xe2x88x925xc2x0 C. to xe2x88x9220xc2x0 C. Chapters 11 and 12 of the Arbuckle reference referred to above details known methods. of producing frozen emulsion products which are easily adapted to produce the frozen emulsions of the invention.
The gel particles may be added to the aqueous continuous phase of the food emulsion in any suitable manner and at any suitable time during the process to produce the emulsion. For example, the gel particles may be added to the otherwise completely formulated food product (that may not contain any other fat components) to produce the final food emulsion. Alternatively, the gel particles may be added to the aqueous continuous phase of the emulsion with at least one of the remaining components of the food emulsion added thereafter.
If the food emulsion is to be subjected to an homogenisation process during its preparation, it is preferred the gel particles are added after homogenisation.
If the food emulsion is to be subjected to a pasteurisation process during its preparation, depending upon the material used to form the gel particles, the particles may be added at any stage during the preparation. For example if a low melting point material such as carrageenan or gelatine is used to produce the gel particles, it is preferred if they are added post-pasteurisation.
The temperature of the gel particles when added to the emulsion or at the least one component thereof is not believed to be crucial, e.g. they may be added at a temperature above or below room temperature, i.e. above or below 25xc2x0 C. However, for economic reasons it is preferred to add the gel particles to the emulsion or its components when the particles and/or emulsion/component(s) are at a temperature below 10xc2x0 C. Preferably the particles and the emulsion/component(s) are at a temperature at or below 10xc2x0 C., most preferably at or below 5xc2x0 C. The particles and/or emulsion/component(s) may be at a temperature below 0xc2x0 C., eg below xe2x88x925xc2x0 C. when the addition occurs. The gel particles and/or emulsion/component(s) may be in a liquid, partially frozen state (ie containing frozen and unfrozen material) or frozen state during the mixing thereof.
It is especially preferred in the manufacture of pasteurised frozen products, eg ice-cream, if the gel particles have a temperature below 10xc2x0 C., preferably below 5xc2x0 C. when added to a pasteurised aqueous phase having temperature conveniently below 10xc2x0 C., but preferably in the range 5xc2x0 C. to 15xc2x0 C.
The flavour molecules may be added to the food emulsion in any suitable manner, and at any suitable time during the process. Typically the flavour is added to the aqueous phase of the emulsion, although at least a proportion of the flavour molecules may be in the gel particles when they are added. The latter option is more suitable to those flavour molecules having a low-volatility.
It is preferred if the flavour molecules are added at room temperature or a temperature below room temperature, e.g. at 30xc2x0 C. or below, preferably 25xc2x0 C. or below. It is especially preferred if the flavour molecules are added cold, e.g. below 25xc2x0 C., preferably below 20xc2x0 C., most preferably below 10xc2x0 C.
When preparing a frozen low-fat emulsion in accordance with the present invention, flavour components need minimal re-balancing to account for the low phase volume of fat. Also, critical flavours, which are normally fat-soluble and therefore particularly prone to uncontrolled release in low fat emulsions during consumption of the product, are released according to their xe2x80x9cfull-fatxe2x80x9d timescale, thereby improving the perception of their flavour.
The present-invention provides means for controlling the transfer rates, including the rate of release, of flavour molecules in a frozen emulsion, thereby allowing manipulation of the flavour release profile of frozen low-fat food emulsions. Hence, low-fat frozen emulsions can be prepared which have the taste of the equivalent full-fat emulsions during consumption. The present invention achieves this without recourse to an encapsulating coating which must be heated or solubilised in order to release encapsulated flavours.
Examples of the products and processes of the invention will now be described to illustrate by way of example only, but not to limit the invention, with reference to the accompanying figures.